Pension and Other Postretirement Benefits, Fair Value of Postretirement Benefit Plans Assets (Details) - Postretirement Benefit Plans [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity securities [Abstract]
Fair value of company's plan assets	$ 61	$ 67	$ 60
Percentage of mutual fund in total investment in fixed income - investment grade securities	82.00%	77.00%
Percentage of pooled bond funds in total investment in fixed income - investment grade securities	18.00%	23.00%
Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	$ 48	$ 53
Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	10	11
Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
U.S. Equity [Member]
Equity securities [Abstract]
Fair value of company's plan assets	35	38
U.S. Equity [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	35	38
U.S. Equity [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
U.S. Equity [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
International Equity [Member]
Equity securities [Abstract]
Fair value of company's plan assets	1	2
International Equity [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	1	2
International Equity [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
International Equity [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Fixed Income - Investment Grade [Member]
Equity securities [Abstract]
Fair value of company's plan assets	11	13
Fixed Income - Investment Grade [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	9	10
Fixed Income - Investment Grade [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	2	3
Fixed Income - Investment Grade [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Fixed Income - High Yield [Member]
Equity securities [Abstract]
Fair value of company's plan assets	4	3
Fixed Income - High Yield [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Fixed Income - High Yield [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	4	3
Fixed Income - High Yield [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Real Estate Investment Trusts [Member]
Equity securities [Abstract]
Fair value of company's plan assets	3	3
Real Estate Investment Trusts [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	3	3
Real Estate Investment Trusts [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Real Estate Investment Trusts [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Other [Member]
Equity securities [Abstract]
Fair value of company's plan assets	4	5
Other [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Other [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	4	5
Other [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Total Assets at Fair Value [Member]
Equity securities [Abstract]
Fair value of company's plan assets	58	64
Other Investments Measured at Net Asset Value [Member]
Equity securities [Abstract]
Liabilities for unsettled trades, net	$ 3	$ 3